With the gradual exhaustion of earth resources and the increase of people's attention to environmental issues, the application of renewable energy resources is increasingly valued by countries around the world. The microgrid is an emerging energy organization mode that increases the permeability of renewable energy resources to provide uninterrupted power supply. The microgrid includes different types of distributed energy resources (DERs, including micro gas turbines, wind driven generators, photovoltaics, fuel cells, energy storages, etc.), user terminals of various electrical loads and/or thermal loads and related monitoring and protection devices.
The internal power supply of the microgrid mainly lies in the energy conversion by power electronic devices, where proper control is indispensable. With respect to the main grid, the microgrid can be considered as a controlled power unit, and meets the requirement of power quality and power supply security. The microgrid is connected to the main grid through the point of common coupling for energy exchange, and the both parties are mutually standby, which improves the reliability of power supplies. Since the microgrid is a small-scale power system and close to the load, it can greatly increase the reliability of power supplies, reduce the network loss and greatly enhance the energy efficiency, which meets the requirements of future development in smart grid.
Droop control algorithm is widely concerned because of the realization of communication-free power sharing, but the output voltage of each distributed generation may suffer from the steady-state deviation. At the same time, voltage droop control typically yields towards a poor performance in the reactive power sharing due to the difference in the output impedance of each distributed generation. Therefore, secondary voltage control is needed to improve the accuracy of reactive power sharing and the voltage performance in the microgrid system. The cooperative voltage control schemes have already undertaken, regarding centralized control and distributed control, both of which rely on communication technologies, However, the communication process is usually affected by information latency and data drop-out, and in the worst case the system stability is affected. Therefore, it is necessary to investigate a decentralized control system that does not rely on remote measurements or real-time communications to carry out reactive power sharing and voltage restoration of distributed generations, thereby improving the stability and dynamic performance of the microgrid and improving the power quality.